Excretory system

• Kidney


  A compound tubular gland covered by a connective tissue capsule
• There is a depression on the medial border of kidney called hilum, through which renal artery, renal veins, nerves and ureter pass
• Different layers of kidney


  • Outer cortex
  • Inner medulla
  • Renal sinus
• Outer cortex

  • Dark and granular in appearance
  • Contains renal corpuscles and convoluted tubules
  • Cortical tissue penetrates medulla in the form of columns called renal columns or columns of Bertin
• Inner medulla


  • Contains tubular and vascular structures arranged in parallel radial lines
  • Divided into 8 to 18 medullary or Malpighian pyramids
  • Broad base of each pyramid is in contact with cortex and the apex projects into minor calyx
• Components of renal sinus

  • Upper expanded part of ureter called renal pelvis
  • Subdivisions of pelvis: 2 or 3 major calyces and about 8 minor calyces
  • Branches of nerves, arteries and tributaries of veins
  • Loose connective tissues and fat
• Kidney

  • Made up of closely arranged tubular structures called uriniferous tubules
  • Blood vessels and interstitial connective tissues are interposed between these tubules
• Uriniferous Tubules

  • Terminal or secretary tubules called nephrons which are concerned with formation of urine
  • Collecting ducts or tubules which transport the urine from nephrons to pelvis of ureter
• Collecting ducts


  1. Unite to form ducts of Bellini

  2. Open into minor calyces through papilla
• Nephron : structural and functional unit of kidney.

  Parts of nephron :

  1. Blind end called renal corpuscles or malpighian corpuscles
  2. Tubular portion called renal tubule
• Function of renal corpuscles is filtration of blood which forms first phase of urine formation
• Renal corpuscles formed by 2 portions :

  Glomerulus

  Bowman's capsule
• role of kidney in homeostasis

  • Excretion of Waste Products
  • Maintenance of Water Balance
  • Maintenance of Electrolyte Balance
  • Maintenance of acid-base balance
• Substances secreted by Kidney

  • Erythropoietin •Thrombopoietin
  • 1,25 - dihydroxycholecalciferol
  • Prostaglandins •Renin
• Cortical nephron


  • Renal corpuscle situated in outer cortex near the periphery
  • Short loop of Henle that penetrates only up to outer zone of medulla
  • 85% of nephrons
  • Blood supply to tubule via peritubular capillaries
  • Function is formation of urine
• Juxtamedullary nephron


  • Renal corpuscle situated in inner cortex near medulla
  • Long loop of Henle that penetrates up to the tip of papilla
  • 15% of nephrons
  • Blood supply to tubule via vasa recta
  • Function is mainly concentration of urine and also formation of urine
• Tubular portion of nephron :

  1. proximal convoluted tubule
  2. loop of henle
  3. distal convoluted tubule
• loop of henle :

  1. descending limb
  2. hairpin bend
  3. ascending limb